Thank you for your answer.
I submitted AOS in February 2023 with an 'original' certified copy of the marriage certificate, as we got a couple of those on hand for cases like this. Therefore, the seal was cleary present. My only thought is that the certified copy mentions the date of marriage indirectly as "Original certificate issued on 01/13/2023 by Marriage Clerk ... Witness my hand and the seal of said Court this 17th day of January, 2023." Do you think this is not clear enough that the day of the marriage was the 13th?
If the RFE should be responded to physically by mail, why do I have the option to answer digitally in the My Uscis portal then? I compiled a new cover letter, the RFE letter, and a copy of both the Marriage Certificate and a Certified Copy thereof, and uploaded this into the portal. I wrote in the cover letter that I would also follow up by sending the same bundle via regular mail to their office local to me (the address they requested was a local field office, not the central office where we submitted our I-485 documents). I hope this way I am thorough enough for either digital or physical requirements, and by stating that the paper copy is coming I hope this will not confuse my caseworker.